Both diploid parents (P) have a pair of redundant genes originating from an ancient genome duplication. In parent A (Col in this case), the blue copy is functional, whereas the red copy is not expressed due to epigenetic silencing. Parent B (Cvi in this case) has a mutation in the blue copy, but it is viable because the red copy is expressed. Hybrids between the parents are viable, but their selfing results in F2 progeny in which individuals homozygous for the mutated and inactivated genes are missing, leading to reduced gene flow and increasing isolation. Passage of the silent red copy through homozygous silencing mutants leads to its stable reactivation also in parent A (Col). Crosses of such a parent with parent B (Cvi) produce F2 progeny with all segregating genotypes present.